This invention concerns apparatus use in the processing of sheet material, particularly, though by no means exclusively, of corrugated Board or card as used in the box and carton making industries.
One aspect of the present invention is concerned with the control of sheet material feed upstream of, and through, the nip between rotating rolls provided with one or more sheet-treatment tooling sets for effecting cutting, printing, creasing and/or scoring etc of the sheet material. In conventional sheet processing machinery, sheet material feed through the nip is imparted by the rotating rolls via tool-sheet engagement and, when the tooling is disengaged from the sheet, via traction belts or the like provided on the rolls. This necessarily imposes limitations on the variety of blank sizes that can be catered for.
According to one aspect of the present invention there is provided apparatus for processing sheet material comprising; a set of rotatable rolls provided with one or more sheet-processing tools for engagement with the sheet material in the nip zone between the roll set; a first drive for rotating the roll set; a second drive upstream of the nip zone for effecting feed of the sheet material; and means operable to co-ordinate operation of the second drive with rotation of the roll set in such a way that sheet feed through the nip zone is effected in part by the roll set and in part by the second drive.
Various features of this aspect of the invention including a related method are the subject of claims appended to this specification.
Another aspect of the invention is concerned with the feed of sheet material to processing machinery in which stacked sheets are placed on a feed table against a gate which allows only the lowermost sheet to pass therebeneath to be taken into the nip of take-up rolls. In known equipment, this may be effected under the action of a reciprocating vacuum suction cup, feed rollers or a kicker mechanism. Such feeding arrangements must be controlled with great precision and even then misfeeds are a not uncommon experience. One solution to these problems is proposed in my British Patent No. 2 274 276, but this involves reciprocating movement of the entire roller bed, which is not energy efficient and places certain restrictions on sheet size.
According to a second aspect of the present invention there is provided for apparatus for feeding sheet material sequentially on demand to take up mechanism of sheet processing machinery, said apparatus comprising a feed surface having a gate and upon which the sheets may be stacked against the gate which allows only the lowermost sheet to pass therebeneath, conveyor means (such as a bed of rollers or a conveyor belt) associated with the feed surface for advancing the lowermost sheet beneath the gate to the take-up mechanism, means to allow the conveyor means to free-wheel once the lowermost sheet is being advanced thereover by said take-up mechanism, and means for restraining freewheeling feed of the next lowermost sheet after the sheet being fed has cleared the conveyor means.
In one embodiment, such freewheeling feed by the conveyor means may be restrained by some form of braking means acting on the next lowermost sheet, e.g. vacuum suction means behind the rollers to hold the next lowermost sheet against the action of the free-wheeling rollers after the sheet being fed has passed under the gate.
In another embodiment, such freewheeling feed by the conveyor means may be restrained by braking means acting on the conveyor means.
The take-up mechanism may comprise take-up rolls.
The conveyor means may comprise rollers fitted with sprag clutches and may advance the sheet being fed at substantially the same speed as or, more preferably, a slower speed than, that of the take-up mechanism.
Vacuum suction may be applied from beneath the conveyor means to pull the lowermost sheet downwardly thereagainst.
A further aspect of the invention is concerned with ensuring that feed of the sheet material is in proper registry with the sheet-treatment machinery.
To this end prior known sheet feeding apparatus has relied upon the leading edge of each sheet being at a defined position at the commencement of feed. Many factors, including premature movement of a sheet by continuing rotation of feed rollers after the previously fed sheet has cleared them, mechanical tolerances, improper stacking of the sheets on the feed table, sheet quality and even atmospheric conditions can cause the leading edge of a sheet to be displaced from the expected defined position at the commencement of feed.
According to a third aspect of the present invention there is provided apparatus for feeding sheet material sequentially on demand to take-up mechanism of sheet processing machinery, said apparatus comprising a feed table having a gate and upon which sheets may be stacked against the gate which allows only the lowermost sheet to pass therebeneath, means driven by a servo-motor to advance the lowermost sheet beneath the gate to the take-up mechanism, a sensing means between the gate and the take-up mechanism to detect the passage of a datum position of the sheet, a microprocessor which receives data indicating the position of the take-up mechanism and from the sensing means and programmed to control the servo-motor to ensure that the sheet presents itself to the take-up mechanism at the correct instant.
The datum on the sheet may be constituted by the leading edge of the sheet or some other suitably positioned mark on the sheet, e.g. printing previously applied to the sheet, a cut-out in the sheet or a print registration mark on the sheet. Prior to sheet treatment involving cutting and/or creasing for instance, it is common practice to apply printing to the sheet for product identification and/or advertising purposes and the subsequent sheet treatment has to be accurately registered with such printing. If the location of the printing is accurately positioned with the leading edge of the sheet and if the leading edge of the sheet has not been damaged in any way, then the leading edge may be used as the datum. However, if print position in relation to the leading edge is not consistent and/or if there is a possibility of the leading edge being damaged, then use of the printing itself as the datum source is to be preferred so that proper registry between the machinery tooling and the printed areas can be secured. Where the datum is derived from pre-applied printing on the sheet, it may be constituted for example by the a leading extremity of a selected part of the printed area.
The microprocessor may also be programmed to ensure that the sheet, or at least the leading edge thereof, presents itself to the take-up mechanism at a desired speed.
The desired speed may be substantially the same as but preferably is slightly less than the speed at which the take-up mechanism forwards the sheet. The desired speed may be substantially zero.
In this aspect of the invention, the take-up mechanism may comprise a pair of take-up rolls or gripper bars and the means driven by the servo-motor may comprise a bed of rollers within the surface of the table which are rotatably driven to advance the lowermost sheet beneath the gate to the take-up mechanism and means to allow the rollers to free-wheel once the lowermost sheet is being advanced thereover by the take-up mechanism.
According to yet another aspect of the present invention there is provided apparatus for feeding sheet material sequentially on demand to take-up mechanism of sheet processing machinery, said apparatus comprising a servo-drive motor, means for transmitting drive from the servo-drive motor to the sheet material to advance the sheet material to the take-up mechanism, sensing means for detecting the passage of a datum position of the sheet material as the latter advances towards the take-up mechanism, and a microprocessor which receives data indicating the position of the take-up mechanism and from the sensing means and programmed to control the servo-drive motor to secure registration between the sheet material and the take-up mechanism, the drive transmitting means being operable automatically in a freewheel mode while in engagement with sheet material travelling at a speed greater than the speed of the servo-drive motor.